The tobacco filter comprising a tow of cellulose ester fiber is in broad use for the purpose of removing the tars from tobacco smoke and yet preserving or keeping the taste and palatability of the smoke. In the production of such a tobacco filter, a plasticizer (e.g. triacetin, triethylene glycol diacetate, triethylene glycol dipropionate, dibutyl phthalate, dimethoxyethyl phthalate, triethyl citrate, etc.) is commonly added for shape retention of the filter plug and for insuring the firmness or hardness necessary for cutting out filter tips from the plug.
In the filter plug formed with the aid of such a plasticizer, the filaments have been partly fused together by the plasticizer. Thus, the plasticizer plays the role of a binder interbonding the cellulose ester filaments at random locations. As a consequence, if the cigaret butt is discarded, it takes a long time for the filter plug to disintegrate itself, doing aesthetic harm to the environment and adding to the pollution problem.
Meanwhile, a paper filter made from creped wood pulp and a tobacco filter comprising a tow of regenerated cellulose fiber are also known. Compared with a filter comprising a tow of cellulose ester fiber, these filters are slightly more wet-disintegratable and, hence, of somewhat lower pollution potential. However, the aroma and palatability of tobacco smoke are sacrificed and the selective removal of phenolic components which is required of any tobacco filter can hardly be expected. Moreover, the firmness of these filters is lower than that of the cellulose ester filter on a given pressure loss basis.
Japanese Patent Application Laid-open No. 24151/1981 (JP-A-56-24151) discloses a filter comprising a cellulose acetate fiber and a hot-melt or temperature-sensitive adhesive fiber bonding said acetate fiber at points of intersection. As the hot-melt adhesive fiber, a fibrillated polyolefin or equivalent fiber is employed and its proportion to cellulose acetate fiber is 25-50 weight %. This filter is substantially not disintegrated in water because the cellulose acetate fiber is three-dimensionally or nodally bonded at a multiplicity of points of intersection by the water-insoluble hot-melt adhesive fiber.
Japanese Patent Laid-open No. 75223/1975 (JP-A-50-75223) corresponding to U.S. patent application Ser. No. 411,117 describes a technology for manufacturing a tobacco filter which comprises bonding a cellulose ester fiber with an adhesive composition consisting of a high-boiling polyol and a water-soluble or -dispersible polymer which is soluble in said polyol as selected from the group consisting of polyesters, polyamides and polyesteramides.
WO 93/24685, directed to a biodegradable tobacco filter comprising a cellulose ester fiber and a photosensitive metal oxide, describes a filter rod (tobacco filter) comprising a tow of the fiber integrated with a water-soluble binder and a water-soluble adhesive for fixing or adhering a wrapping paper which wraps the tow.
As described in these literature, a water-soluble adhesive agent in the form of a solution in water or a hydrophilic solvent is applied to the fiber by spraying or dipping but there is no reference to importance of the amount of water used with respect to the cellulose ester fiber.
Meanwhile, a filter rod is generally manufactured by wrapping a tow of cellulose ester or other fiber in wrapping paper at a high speed of, for example, about 400 m/min. Therefore, in the manufacture of a filter rod, the tow should be compatible with the high speed of processing, particularly that of wrapping operation.